Ashkenazi Jews & Intelligence
Freud, Einstein, Mahler
Kristy Brady8 February 2006
Outline
• Heterozygote advantage • Example: sickle-cell anemia & malaria• A brief history of Ashkenazi Jews• Observations on Ashkenazi Jew
intelligence & disease• Hypothesis correlating intelligence &
disease• Proposed evolutionary mechanisms• Alternative hypotheses
Heterozygote Advantage
(aka: overdominance)
• A case in which heterozygotes have a higher fitness than homozygotes at a given locus. Maintains genetic polymorphism in a population.
− e.g., sickle-cell allele & malaria tolerance
− e.g., cystic fibrosis allele & TB resistance
Distribution of sickle-cell anemia & malaria
Green: regions with malaria
Red stripes: regions with high frequency of sickle-cell trait
Genotypes (S = wild-type allele, s = sickle-cell allele)
SS: no sickle-cell trait, not malaria tolerant
Ss: no sickle-cell disease, malaria tolerant
ss: sickle-cell disease
Heterozygote Advantage
sickle-cell malaria
Ashkenazi Jews: Observations
• Have the highest average IQ test scores of any ethnic group (for which there are data).
• During the 20th century, comprised ~3% of the U.S. population, but won 27% of Nobel prizes awarded to U.S. scientists.
• Represent over half of the world chess champions.
• High incidence of sphingolipid storage diseases: Tay-Sachs, Gaucher, Niemann-Pick.
• High incidence of certain cancers (DNA repair cluster mutations).
Ashkenazi Jews: A brief history
• 3 Jewish groups: Ashkenazi (blue), Middle Eastern (green), Sephardic (red)
• Ashkenazi Jews (from Hebrew word for German) moved north of Alps in 1st millennium A.D. Settled in Rhineland during 800s.
• In 12th & 13th centuries, expelled from Western Europe. Moved to Poland & Lithuania where Ashkenazi center remained for 5 centuries.
Ashkenazi Jews: A brief history
• In 19th & 20th centuries, large migration to W. Europe, Americas, Australia, & South Africa
Sphingolipid Storage Diseases – neurological disorders
Sphingolipids: A member of a class of lipids derived from the aliphatic amino alcohol sphingosine. They play an important role in signal transmission and cell-cell recognition.
•Gaucher: accumulation of sphingolipid that promotes growth & branching of axons.
•Niemann-Pick & Tay-Sachs: accumulation of sphingolipids that promote growth of dendrites.
Hypothesis•Heterozygote advantage (e.g., Gaucher
allele, recessive)
– GG: wild-type
– Gg: no disease, moderate increased linkage between brain cells yields increased intelligence
– gg: Gaucher disease, increased linkage between brain cells yields increased intelligence (as measured by IQ tests)
•Similar scenarios for heterozygotes with Niemann-Pick or Tay-Sachs alleles.
Evolutionary mechanisms
•Selective pressures
− money-related occupations (e.g., banking, tax farming); today IQ and success are positively correlated in these professions
•Assortative mating/no gene flow
– Ashkenazim tend to marry among themselves
Evolutionary mechanisms•Fitness
– in Europe, prior to the 18th century, affluent families tended to have more children surviving to adulthood than poorer families
•Effective population size– ~40% of Ashkenazi Jews
are descended from 4 women living sometime in the last 2,000 yrs (Am. J. Hum. Gen. 2006, 78:487-97)
Evolutionary mechanisms
•Heritability of IQ– in youth “in impoverished families, 60% of the
variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse.” (Psych. Sci. 2003, 14:623-8)
– in youth “past experiences…influence today’s IQ only because of their effect on past IQ and the effect of past IQ on today’s environment” (Psych. Rev. 2001, 108:346-69)
– adult IQ largely affected by adult environment (Psych. Rev. 2001, 108:346-69)
Alternatives to selection?
•Genetic drift
– evidence of genetic bottleneck
•Diet
– quantity of omega-3 fatty acids consumed by a pregnant mother greatly influences a child’s verbal IQ & social skills
•Culture
– education highly valued
Potential Experiments
• IQ tests controlled for genotypes
• Environmental effect studies
– dietary controls